A track is formed in a recording area on a recording medium (optical disc) such as a DVD+R disc, a DVD+RW disc, etc. The track plays a role of a guidance groove for a spot of a laser light irradiated for recording and reproduction of information.
The wobble (meandering) is formed in the track, and since a wobble signal detected from the wobble has a substantially fixed cycle, the detected wobble signal is mainly used as rotating-speed information.
Moreover, information other than the above-mentioned rotating-speed information may also be stored in the track by modulating the wobble.
As information stored by the wobble, address information indicative of an absolute position on a recording medium is most popular.
Additionally, there are listed a recording type indicative of feature of the recording medium, that is, a size of the recording medium or whether the recording medium is a write-once-read many type or an overwrite type, information of recording property, that is, parameters such as an optimum recording power, a recording waveform or the like, and information such as a manufacture's name.
Next, a description will be given of a format of the wobble of each of CD system recording media (CD-R disc, CD-RW disc, etc.) and DVD+ system recording media (DVD+R disc, DVD+RW disc, etc.).                The CD system recording medium: biphase-modulating address information and wobbling a track with a frequency modulation based on it (for example, refer to Japanese Laid-Open Patent Application No. 9-212871).        
Specifically, in the CD system recording medium, two kinds frequencies of 22.05 kHz±k Hz are assigned to data o and data 1, respectively, so as to record information using the wobble of about 10 cycles for one bit. Moreover, probabilities of generation of the data 0 and the data 1 are caused to be substantially equal to each other so as to detect a clock signal from 22.05 kHz, which is the center frequency.                The DVD+system recording medium: phase-modulating address information and wobbling a track base on it.        
In the DVD+ system recording medium, a carrier component is extracted from a carrier wave wobble of a carrier wave area, which occupies a large part so as to detect a clock signal. The address information is recorded in an address area by setting a wobble of the same phase with the carrier wobble as data 0 and setting a wobble of a phase different from the carrier wobble by 180 degrees as data 1.
However, there was a problem as shown below, respectively, in the wobble of the CD system recording medium and the DVD+ system recording medium mentioned above.
In the format of the wobble of the CD system recording medium, since the clock signal of 22.05 kHz is extracted and a frequency difference representing the data 0 and data 1 is extremely small as ±1 kHz, S/N of the signal was low and information recording quality was not good. Moreover, it is difficult to accurately specify a frequency change point, and there was a demerit that an absolute position accuracy was poor.
On the other hand, in the format of the wobble of the DVD+ system recording medium, S/N of a signal can be raised by using a phase modulation. Moreover, absolute position accuracy is also assured, and an advance format has been achieved.
However, since the modulation methods of the wobble for synchronization and the wobble for information are the same and the synchronization signal and the information signal are distinguished by a difference in the phase inverted wobble length, it takes a time to pull-in synchronization. Moreover, since information is recorded by the same cycle and only the phase modulation, leakage of a wobble component between adjacent tracks appears remarkably in degradation of information signal, and it was difficult to progress further high-densification of narrow track pitch while achieving both acquisition of reliability of information and acquisition of recording quality.